In FIG. 1, there is illustrated a schematic of a prior art, four color liquid electrophotography system. A pair of rollers 10 and 12 support and move an organic photoconductor (OPC) belt 14. A laser beam 16 image-wise exposes OPC belt 14 as it passes around roller 12. Exposed areas of OPC belt 14 are then passed through developer modules 18. In the known manner, OPC belt 14 requires four passes through developer modules 18 so as to achieve a superimposition of four color planes which comprise the color image (i.e. cyan, magenta, yellow and black). Until all four passes are accomplished, a transfer roller 20 is maintained out of contact with OPC roller 12. However, after the final pass of OPC belt 14 through developer modules 18, transfer roller 20 is brought into contact with OPC belt 14 so as to enable a transfer of the image from OPC belt 14 to the surface of transfer roller 20. A sheet of paper 22 is then passed between transfer roller 20 and a heated pressure roller 24 to allow transfer of the image from transfer roller 20 to paper sheet 22.
Subsequent to transfer of the image from OPC belt 14 to transfer roller 20 and thence to paper 22, a fifth pass occurs to enable OPC belt 14 to be cleaned of residual toner. It has been found that some toner collects just past the image area during the toning process. Such toner is not removed until the fifth cleaning pass. If such residual toner is allowed to contaminate transfer roller 20, it can be later transferred to paper sheet 22 and ruin any image thereon. While transfer roller 20 may be controlled to separate from OPC roller 12 and OPC belt 14 at the end of the image (thus avoiding contact with residual toner following the image), because a substantial portion of the image still resides on transfer roller 20 that has not yet been emplaced on paper sheet 22, the pressure between transfer roller 20 and pressure roller 24 must still be maintained unchanged until the image transfer function is complete.
During a print operation, the temperature and pressure at the point of contact between OPC roller 12 and transfer roller 20 are maintained at approximately 50.degree. C. and at a pressure of approximately 50 pounds. These conditions assure appropriate transfer of the toner from OPC belt 14 to transfer roller 20.
By contrast, pressure roller 24 is heated to maintain its point of contact with transfer roller 20 (and paper sheet 22) at between 100.degree.-150.degree. C. at a pressure of approximately 200 pounds. If transfer roller 20 and pressure roller 24 are maintained in contact when no printing action is in process, the elevated temperature of pressure roller 24 can cause the temperature of transfer roller 20 to elevate to an unacceptable level. Thus, when no printing action is in process, pressure roller 24 should be separated from transfer roller 20 to assure relative temperature isolation therebetween (and also to avoid creation of a pressure set in the transfer roller).
Accordingly, it is an object of this invention to provide an improved system for the control of roller contact in a liquid electrophotography system.
It is an other object of this invention to provide a liquid electrophotography system with an improved roller positioning system that requires only a single actuation mechanism.
It is a further object of this invention to provide electrophotography system with an improved roller contact control mechanism wherein contamination of a transfer roller by residual color toner is avoided.
It is yet another object of this invention to provide an improved mechanism for control of roller positioning in a liquid electrophotography system wherein substantial temperature isolation between rollers is assured.